Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR SAMPLING AN EAR
FORMATION THROUGH A CASED BOREHOLE
FIELD OF THE INVENTION
This invention relates to the field of investigating formations surrounding
earth boreholes. More particularly, this invention relates to perforating a
cased
borehole, measuring the pressure, sampling fluids in the earth formation
surrounding the cased borehole and resealing of perforations in the casing.
BACKGROUND OF THE INVENTION
Although there exists an ever increasing demand to find oil and gas
reserves, there are approximately 200 wells considered for abandonment each
year in North America which adds to the thousands of wells that are already
idle. These abandoned wells have been determined to no longer produce oil
and gas in necessary quantities to be economically profitable. However, the
majority of these wells were drilled in the late 1960's and 1970's and logged
using techniques that are primitive by today's standards. Thus, recent
research
has uncovered evidence that many of these abandoned wells contain large
amounts of recoverable natural gas and oil (perhaps as much as 100 to 200
trillion cubit feet) that have been missed by conventional production
techniques.
Because the majority of the field development costs such as drilling, casing
and
cementing have already been incurred for these wells, the exploitation of
these
wells to produce oil and natural gas resources could prove to be an
inexpensive venture that would increase production of hydrocarbons and gas.
In well logging, to determine whether there are retrievable resources, the
most important parameter that a reservoir engineer uses to manage a well is
downhole pressure. Normally, a borehole is logged (pressure measurements
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23 9i~~2
and fluid samples) immediately after drilling (open hole) to locate primary
and
secondary pay zones. However, in the drilling and/or producing of an earth
formation borehole steel casing may be routinely used in one or more sections
of the borehole to stabilize and provide support for the formation surrounding
the borehole. Cement is also employed on the outside of the casing to hold the
casing in place and to provide a degree of structural integrity and a seal
between the formation and the casing.
There are various circumstances in which it is necessary or desirable to
make one or more perforations through the casing and cement in order to
retrieve resources from the formation and to perform tests behind the casing
and through the surrounding cement, if present. For example, a commercially
used technique employs a tool which can be lowered on a wireline to a cased
section of a borehole, the tool including a shaped explosive charge for
perforating the casing, and testing and sampling devices for measuring
hydraulic parameters of the environment behind the casing and/or for taking
samples of fluids from said environment.
During the production of a well and after the primary pay zone is
depleted, a series of shaped-charge explosives are lowered into the well and
the casing at the secondary zone is perforated. Currently, this perforation
technique is also used to gain pressure and porosity information during
exploration behind casing in older wells. However, if the zone does not posses
hydrocarbons or sufficient pressure, the perforation holes must be sealed to
prevent crossflow between layers of fluids.
In addition, based on results of testing after through perforations in
casing, sometimes a decision is made whether to perforate the well for
production or to abandon and plug or reseal the zone. The term "plugging"
traditionally means plugging an entire cross section of the well. Perforations
can be plugged with cement through drill pipes. Elastomeric
plugging is also used to plug an entire well by isolating the zone below the
plug
during or after the production. Elastomeric plugs-are also used as an anchor
for
setting cement. Well treatment and plugging can also be done with coiled
tubing. Plugging a perforation to prevent crossflow between layers of fluids
involves using an explosive, difficult and time-consuming process called a
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2 ~ 91962
"squeeze job" which consists of isolating the perforated zone and squeezing
cement into the perforations.
A drawback of using a tool that perforates casing for testing is that the
perforation which remains in the casing can cause problems in instances where
production or zone plugging does not quickly follow. In some fortunate
instances the perforation may become clogged with debris from the borehole
and rendered essentially harmless if the debris permanently plugs the
perforation. However, if the perforation, or part of it, remains open, a
substantial
volume of formation fluids may be lost into the formations and/or may degrade
the formation. In some situations, fluids from the formations may enter the
borehole with deleterious effect. Gas intrusion into the borehole can be
particularly problematic.
Not only are there problems plugging a perforation in casing, there can
be problems in the actual perforating of the casing. One major problem with
perforating the casing is that current perforating means include shape-charge
explosives. The use of these explosives usually produce non-uniform
perforations in the casing. Therefore, these perforations are difficult to
plug and
often require use of a solid plug and a non-solid sealant material. This
requirement increases the complexity and time required to adequately plug a
perforation in the casing.
An example of the present technology and sampling configuration is
shown in U.S. Patent 5,195,588 (Dave). In this patent, an apparatus is
disclosed that plugs a perforation in the casing. The method of sampling
reveals the above-described limitation for sampling at extended depths into
the
earth formation. Dave describes a perforating technique that incorporates a-
shaped-charge to create a perforation in the casing. Although the Dave patent
mentions perforating and sampling in a cased hole, there is virtually no
discussion in Dave about techniques that create more uniform perforations or
about techniques that extend the depth of sampling into the formation. In
addition, although the Dave patent is similar to the present invention, Dave's
objectives are concerned with developing techniques to be used in plugging an
already existing perforation in the casing. Therefore, there still remains a
need
3
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to create more uniform perforations and to extend sampling capabilities
greater
depths of investigation into the formation.
It is among the objects of the present invention to address the problems
of perforating and testing in cased sections of an earth borehole, and to
design
an apparatus and method which solves the problem in a practical way.
SUMMARY OF THE INVENTION
It is an object of the invention to create more uniform perforations in
casing of a borehole.
It is an object of this invention to create perforations with lengths greater
than the diameter of the borehole.
It is another object of this invention measure pressure and sample
formation fluids through borehole casing.
It is another object of this invention to plug and reseal borehole casing
perforations.
In accordance with a form of the present invention, there is provided an
apparatus and method for perforating and resealing casing in an earth
borehole. The apparatus also has the capability to sample and test the earth
formation fluids. The apparatus is moveable through the casing and can be
mounted on a wireline, on tubing, or on both. Mounted inside the apparatus is
a
perforating means for creating a perforation through the casing and into the
borehole. The plugging means is also mounted inside the device for plugging
the perforation. A plurality of plugs can be stored in the apparatus to permit
the
plugging of several perforations during one tool run in the borehole. The
apparatus will also generally include means for testing/sampling (that is,
testing
for hydraulic properties such as pressure or flow rate, and/or sampling
fluids) of
the fluids of formations behind the casing.
In an embodiment of the invention, the perforating means comprises a
flexible shaft to be used to drill a perforation through the casing and
formation.
The flexibility of the flexible shaft permits drilling a perforation into the
formation
at lengths greater than the diameter of the borehole and thereby enables the
4
70261-67 CA 02197962 2004-11-09
sampling at formation depths greater than the borehole
diameter. Plugging means are also mounted in the device for
plugging the perforation. In an embodiment of the
invention, the means for plugging the perforation comprises
means for inserting a plug of a solid material into the
perforation.
To secure the apparatus in the borehole, this
invention also has a means for setting said device at a
substantially fixed location. The invention also has the
capability of actuating the perforating means and the
plugging means while the device is set at a substantially
fixed location. Also this embodiment can have a means for
moving the perforating means to a desired position in the
borehole. There is also a means for moving the plugging
means to a position opposite the perforation in the casing.
Although this invention contains some known
features, there are several advantages to the present
invention over the existing technology. First, this
invention uses non-explosive perforating means to perforate
the casing that creates a more uniform perforation which can
be easily plugged and without the need to use of non-solid
plugging means. Another advantage is the ability to extend
the perforation to lengths in the formation that are greater
than the diameter of the borehole. A major advantage of the
present invention is that it can be implemented with a
wireline device and does not require tubing, although tubing
can be used if desired. Another result of this advantage is
more flexibility in aligning a motor and power devices. A
further advantage of a form of the present invention is that
a perforation can be plugged while the tool is still set in
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70261-67 CA 02197962 2004-11-09
the position at which the perforation was made, so the
plugging operation can be specifically and accurately
directed to the perforation, without the need for locating
the perforation or for wasting the plugging medium by
plugging a region that is larger than the perforation
itself .
The invention may be summarized according to a
first broad aspect as an apparatus for sampling an earth
formation at extended formation depths from a cased borehole
environment, comprising: a means for creating a perforation
in said casing, said perforating means being capable of
extending said perforation into said formation at depths
greater than the diameter of said borehole; a plugging means
for plugging said perforation by inserting a plug of solid
material into said perforation; a means for hydraulic
testing and sampling said formation at said extended
formation depths via said perforation; and a housing
moveable through the casing and in which said perforating
means, plugging and testing means are mounted.
According to a second broad aspect the invention
provides an apparatus for sampling an earth formation at
extended formation depths from a cased borehole environment,
comprising: a non-explosive means for creating a perforation
in said casing and capable of extending said perforation
into said formation at depths greater than the diameter of
said borehole; a means for hydraulic testing and sampling
said formation at said extended formation depths via said
perforation; and a housing moveable through the casing and
in which said perforating means and said testing means are
mounted.
5a
70261-67 CA 02197962 2004-11-09
According to a third broad aspect the invention
provides a method for sampling an earth formation at
extended formation depths from a cased borehole traversing
said formation, comprising the steps of: moving a device to
a position in a region of said borehole; setting said device
at said position in the borehole; perforating said casing
and formation using non-explosives such that a perforation
is created, said perforation extending into said formation
to depths greater than the diameter of said borehole;
establishing fluid communication between said device and
said perforation while said device is set at said position;
and obtaining a formation fluid sample through said
perforation.
Further features and advantages of the invention
will become more readily apparent from the following
detailed description when taken in conjunction with the
accompanying drawings.
5b
2i~7~~~
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an apparatus in accordance with the
present invention and which can be used to practice the method of the
invention.
FIG. 2 is a flow diagram of a routine for controlling operation of
embodiments of the invention.
FIG. 3 a view of a conventional drill bit system for creating a perforation
and plugging the perforation.
FIG. 4a is a diametrical tool section of a flexible drilling shaft in
accordance with the present invention.
FIG. 4b is a longitudinal tool section of a flexible drilling shaft in
accordance with the present invention.
FIG. 5 is one of a pair of mating guide plates.
FIG. 6a is side view of the components of a plugging assembly.
FIG. 6b is side view of the components of a plugging assembly during
the plugging operation.
FIG. 6c is a side view of a plug hole in the casing using the plugging
assembly of the present invention.
FIG. 7 is a side view of the mechanical plugger and plug magazine.
6
~i~i~6
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 shows one embodiment of the invention and Fig. 2 illustrates the
flow sequence of operations of the invention. The tool 12 is suspended on a
cable 13, inside steel casing 11. This steel casing sheathes the borehole 10
and is supported with cement 10b. The borehole 10 is typically filled with a
completion fluid or water. The cable length substantially determines the
depths
to which the tool 12 can be lowered into the borehole. Depth gauges can
determine displacement of the cable over a support mechanism (sheave wheel)
and determines the particular depth of the logging tool 12. The cable length
is
controlled by a suitable known means at the surface such as a drum and which
mechanism (not shown). Depth may also be determined by electrical, nuclear
or other sensors which correlate depth to previous measurements made in the
well or to the well casing. Also, electronic circuitry (not shown) at the
surface
represents control communications and processing circuitry for the logging
tool
12. The circuitry may be of known type and does not need to have novel
features. The block 800 in Fig. 2 represents bringing the tool 12 to a
specific
depth level.
In the embodiment of Fig. 1, the tool 12 shown has a generally cylindrical
body 17 which encloses an inner housing 14 and electronics. Anchor pistons
15 force the tool-packer 17b against the casing 11 forming a pressure-tight
seal between the tool and the casing and serving to keep the tool stationary
block 801.
The inner housing 14 contains the perforating means, testing and
sampling means and the plugging means. This inner housing is moved along
the tool axis (vertically) by the housing translation piston 16. This movement
positions, in succession, the components of each of these three systems over
the same point on the casing.
7
A flexible shaft 18 is located inside the inner housing and conveyed
through guide plates 14b (also see Fig. 5) which are integral parts of this
inner
housing. A drill bit 19 is rotated via the flexible shaft 18 by the drive
motor 20.
This motor is held in the inner housing by a motor bracket 21, which is itself
attached to a translation motor 22. The translation motor moves the inner
housing by turning a threaded shaft 23 inside a mating nut in the motor
bracket
21. The flex shaft translation motor provides a downward force on the flex
shaft
during drilling, thus controlling the penetration. This drilling system allows
holes to be drilled which are substantially deeper than the tool diameter.
This
drilling operation is shown in block 802.
Technology does exist that can produce perforations of a depth
somewhat less than the diameter of the tool. One of these methods is shown in
Fig. 3. In this approach the drill bit 31 is fitted directly to a right-angle
gearbox
30, both of which are packaged perpendicular to the axis of the tool body. As
shown, the gearbox 30 and drill bit 31 must fit inside the borehole. In this
FIG.
2, the length of a drill bit is limited because the gearbox occupies
approximately
one-half the diameter of the borehole. This system also contains a drive shaft
32 and a flowline 33.
For the purpose of taking measurements and samples, a measurement-
packer 17c and flow line 24 are also contained in the inner housing. After a
hole has been drilled, the housing translation piston 16 shifts the inner
housing
14 to move the measurement-packer into position over the drilled hole. The
measurement packer setting piston 24b then pushes the measurement packer
17c against the casing thereby forming a sealed conduit between the drilled
hole and flowline 24 as shown in block 803. The formation pressure can then
be measured and a fluid sample acquired, if that is desired 804. At this
point,
the measurement-packer is retracted 805.
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2 ~ 97 yb~
Finally, a plug magazine 26 is also contained in the inner housing 14.
After formation pressure has been measured and samples taken, the housing
translation piston 16 shifts the inner housing 14 to move the plug magazine 26
into position over the drilled hole 806. A plug setting piston 25 then forces
one
plug from the magazine into the casing, thus resealing the drilled hole 807.
The integrity of the plug seal may be tested by once again moving the inner
housing so as to re-position the measurement-packer over the plug, then
actuating this packer hole 808 and monitoring pressure through the flowline
while a "drawdown" piston is actuated dropping and remaining constant at this
reduced value. A plug leak will be indicated by a return of the pressure to
the
flowline pressure found after actuating the drawdown piston. It should be
noted
that this same testing method can be used to verify the integrity of the tool-
packer seal before drilling commences. However, for this test the
measurement-packer is not set against the casing, thus allowing the drawdown
to be supported by the tool-packer. The sequence of events is completed by
releasing the tool anchors 810. The tool is then ready to repeat the sequence
starting with block 800.
Detailed Description of Invention Components
Flexible Shaft
The flexible drilling shaft is shown in detail in figures 4a and 4b and one
of the pair of flexshaft guide plates is shown detailed in Fig. 5. In Fig. 4a,
a
diametrical tool cross-section view, shows the flexshaft and drill bit in the
tool
body 17. The drill bit 19 is connected to the flex-shaft 18 by a coupling 39.
The coupling can be swaged onto the flex shaft. Guide bushings 40 enclose
and hold the drill bit to keep the drill bit straight and in place. Fig. 4b is
a
longitudinal tool section that shows the advantage of a flexshaft over
conventional technology. Figure 5 shows one of the two mating guide plates
42 which form the "J" shaped conduit 43 through which flexshaft is conveyed.
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70261-67 CA 02197962 2004-11-09
The flexshaft is a well known machine element for
conveying torque around a bend. It is generally constructed
by helically winding, in opposite directions, successive
layers of wire over a straight central mandrel wire. The
flex shaft properties are tailored to the specific
application by varying the number of wires in each layer,
the number of layers, the wire diameter and the wire
material. In this particular application the shaft must be
optimized for fatigue life (number of revolutions), minimum
bend radius (to allow packaging in the given tool diameter)
and for conveying thrust.
Another concern is the shaft reliability when
applying thrust to the drill bit through the shaft. During
drilling operations various amounts of thrust are applied to
the drill bit to facilitate drilling. The amount of thrust
applied depends on the sharpness of the bit and the material
being drilled. Sharper bits only require the application of
minimum thrust through the flexible shaft. This minimum
thrust has virtually no affect on the reliability of the
flexible shaft. Duller bits require the application of more
thrust that could damage the flexible shaft. One solution
is apply the thrust directly to the drill bit instead of
through the flexible shaft. In this method, force applied
to a piston located in the tool is transferred by the piston
to the drill bit. The thrust necessary for drilling is
supplied without any effect on the flexible shaft. This
technique is further described in U.S. Patent No.
5,687,806. A second solution is to use a sharp bit each
time a drilling operation occurs, Multiple bits can be
stored in the tool and a new bit used for each drilling
70261-67 CA 02197962 2004-11-09
procedure. As previously stated, the amount of thrust
required by sharper bits has minimal affect on the flexible
shaft. This technique is further described in U.S. Patent
No. 5,746,279.
l0a
~~y7~b~
guideplates
When the flexshaft is used to convey both torque and thrust, as it is in this
application, some means must be provided to support to the shaft to present it
from buckling from the thrust loading applied through the flexshaft to the
drill bit.
In this embodiment of the invention, this support is provided by the mating
pair
of guide plates Fig. 5. These plates form the ~J° shaped conduit
through which
the flexshaft passes. Forming this geometry from a pair of plates is a
practical
means of fabrication and an aid in assembly, but is not strictly necessary for
functionality. A "J" shaped tube could serve the same function. The inner
diameter formed from the pair of plates is only slightly larger than the
diameter
of the flexshaft. This close fit minimizes the helical windup of the flexshaft
in
high torque drilling situations and it also maximizes the efficiency with
which
torque can be conveyed from the drive to the drill bit. The guideplate
material is
chosen for compatibility with the flexshaft. A lubricant can be used between
the
flexshaft and the guideplates.
drillbit
The drillbit used in this invention requires several traits. It must be tough
enough to drill steel without fracturing the sharp cutting edge. It must be
simultaneously hard enough to drill abrasive formations without undo dulling.
It
must have a tip geometry giving torque and thrust characteristics which match
the capabilities of the flexible drive shaft. It must have a fluting capable
of
moving drill cuttings out of a hole many drill-diameters deep. The drill must
be
capable of drilling a hole sufficiently straight, round and not oversized so
that
the metal plug can seal it.
11
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plugging mechanism
The plugging mechanism is shown in figures 6a, 6b and 6c. This
plugging technique has a similar plugging concept to that of U.S. Patent
5,195,588, however, the plug is different. The plug is composed of two
components: a tubular socket 76 and a tapered plug 77. The tubular socket 76
has a closed front end, a lip 78 at its rear and grooves 79 in its center. The
tapered plug 77 is inserted in the opened end of the socket component 76.
The lip 78 serves to hold the socket and prevent it from going past the casing
wall when force is applied to the tapered plug component while it is inserted
into the socket.
Setting the plug is a two stage process. As the piston moves forward the
socket component 76 is forced into the socket component as shown in Fig. 6c.
The tapered nature of component 77, forces the socket 76 to radially expand
thus creating a tight seal between the socket and casing surface. The grooves
79 also help form a seal, and prevent the plug from blowing out. The presence
of more than one groove permits the socket to more readily conform to the
periphery of an irregular perforation in the casing 11 while still ensuring a
good
seal.
Fig. 7 shows the mechanical plugger that inserts a plug into a perforation.
The plugger contains a two stage setting piston (outer piston 71 and inner
piston 80). During the plugging process, as force is applied to both pistons,
71
and 80, the entire piston assembly moves a distance through space 81 forcing
the plug assembly 76 and 77 into the perforation. When the lip portion 78 of
the socket component 76 reaches the casing, the movement of the outer piston
71 stops. The continued application of hydraulic pressure upon the piston
assembly causes the inner piston to overcome the force of the springs 82.
Thus, the inner piston 80 continues to move forcing the tapered plug 77 into
the
socket 76.
12
_ ~i~7962
Fig. 7 also shows the magazine 85 that stores multiple plugs 84 and
feeds them during the plugging process. After a plug is inserted into a
perforation, and the piston assembly 71 and 80 is fully retracted, another
plug
is forced upward and into position to be inserted into the next perforation
that is
to be plugged. This upward move is induced by the force from the pusher
assembly 83. This force can be generated by a spring 86 or fluid.
The method and apparatus of the present invention provides a significant
advantage over the prior art. The invention has been described in connection
with the preferred embodiments. However, the invention is not limited thereto.
Changes, variations and modifications to the basic design may be made without
departing from the inventive concept in this invention. In addition, these
changes, variations modifications would be obvious to those skilled in the art
having the benefit of the foregoing teachings contained in this application.
All
such changes, variations and modifications are intended to be within the scope
of the invention which is limited by the following claims.
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